Extra police patrols are being carried out in Sheffield following a spate of high-value thefts.
South Yorkshire Police said over recent weeks, there has been a rise in the number of burglaries where thieves have broken into homes specifically to take keys for cars parked outside.
High value cars, in particular Audis, have been targeted.
Temporary Detective Inspector John Wheaton said: “We are seeing an emerging trend where high value vehicles have been targeted.
“My advice is that if you own this type of car, or any vehicle for that matter, there are measures you can take to reduce your chances of being targeted.
“If you own a garage, lock your car in your garage and use a steering lock which is a deterrent.”